2 Type R 12's (aero help!!)

Im going to make a box for two alpine type R 12" subs. It will be 42x17x14.5 (externally) With sub displacement included, that gives me a volume of about 4.5^3ft.
I think I want it tuned to about 33hz because I want them to get pretty low, but still sound loud.
Now you all come in. I want to do aero ports, but I dont know how much port volume is needed.
What do you all recommend I use?
4",6",8" 1,2,3 ports?

Re: 2 Type R 12's (aero help!!)

i found that 35hz is best with R's. you aren't going to get much lower with type R's. they get plenty low enough at 35hz, and seem to sound louder (could be psychological more than anything) than lower tunings. if you're using actual flared aero's, a single 6 or double 4 inch port works good.